In performing work on a lathe equipped with a multi-jaw chuck it is often necessary to align the work so that the axis of the work is parallel with the axis of the lathe. By way of example, a work-piece shaped approximately like a flat disk has a virtual axis. This virtual axis is a line perpendicular to the plane of the disk. In order to machine this part correctly, the disk should be placed in the jaws of the lathe so that its axis is parallel with the lathe axis. A sleeve also has an axis which is a line centered in an parallel to the sleeve itself. In order to perform a machine operation, such as machining the outer, peripheral surface of the sleeve after it has been bored and turned, it is necessary to clamp the sleeve in the multi-jaw chuck such that its axis is parallel to the axis of the lathe. Similarly, rings, spacers and various other parts should be aligned to be parallel to the axis of the lathe in the jaws of the lathe.
The usual method, which is generally known and practiced, for aligning work in a multi-jaw chuck, is to place two parallel supports against the front flat surface of the chuck between the jaws of the chuck. The work-piece is then placed against the parallel supports. This process entails considerable time and effort. The operator must simultaneously: 1. hold the parallel supports spaced apart with their narrow edge against the chuck and the work-piece; 2. hold the work-piece flatly on the parallel supports; and 3. close the chuck jaws on the work-piece. If a lot of work is to be finished, the task of aligning the work-piece in the jaws becomes a tedious and time consuming part of the production.
Further, if the parallel supports are not removed from the chuck before lathe operation is begun, they can be propelled at a high rate of speed, as is common in the art.
Since the edge of the disk thin and relatively weak compared to the leveraged force applied by the jaws of the chuck, it is often difficult to align the disk in the jaws of the chuck so that the axis of the disk is parallel to the axis of the lathe. In addition, it is well known in the art that it is difficult to properly align disks in the jaws of a chuck. Improper alignment leads to non-uniform thickness and uneven cuts on the work-piece.
Referring to FIG. 1, a conventional three jaw chuck as known in the machine tool art is shown. The chuck 4 is shown holding a disk work-piece 6. The chuck is fitted on a lathe 7 which is partially shown. The chuck comprises three jaws 1,1' (two are seen in the view of the figure) which are spaced equally about the body 3 of the chuck 4. The jaws are slidably moveable along tracks 8 to expand and contract radially so that they can be adjusted to the proper alignment and hold a work-piece such as the disk 6. The jaws are moved by turning an adjustment screw 2 located on the body 3 of the chuck. Bore 5 is located in the center of the chuck 4.
The disk 6 is clamped in the chuck 4 so that it is skewed and not perfectly square in the chuck 4. As stated above this error is not easily avoided, particularly in the case of fragile parts such as a thin disk work-piece. Arrow C in the drawing represents the axis of the lathe, which is the virtual axis about which the spindle and chuck of the lathe rotate. Arrow P in the drawing represents the axis of the work-piece that is the centerline or axis of symmetry of the work-piece. As shown in the drawing the axis of the work-piece and the axis of the lathe are not parallel.
As shown in FIG. 1 the disk has been clamped in the jaws 1 so that the axis of the disk is not parallel with that of the lathe. An imaginary plane through the points of the jaw in contact with the disk is not perpendicular to the axis of the lathe. The degree to which it is skewed has been exaggerated for the purpose of clarity. In actuality, a disk could be skewed so minimally that the skew could not be observed by the operator but the work-piece would still be incorrectly machined because of the skew. For example, if the outer, planar surface of the disk 6, as shown in FIG. 1, were being machined, the resulting work-piece would have a varied thickness rather than the desired uniform thickness.
U.S. Pat. No. 3,032,347 to Cameron discloses a chuck stop comprising a hub and three radially projecting arms. The draw plug of a lathe is threaded into a threaded hole within the hub, thereby securing the chuck stop on the chuck. Threaded holes on the radially projecting arms are provided to secure spacer members, attached thereto, thereby providing variable axial placement for a work-piece to be machined.
The chuck stop according to the '347 patent is disadvantageous in that the chuck stop prevents the jaws of the chuck from closing and holding work-pieces whose radial dimensions are less than that of the hub. That is, the jaws of the chuck are restricted by the radial dimensions of the hub.
Cameron relies on spacer members to provide axial location of the work-piece. Different sized spacer members are provided in an economically reasonable number thereby prohibiting precise adjustment of the axial location of the disk as is necessary for accurately machining a work-piece disk.
Cameron uses a dark screw which is relatively small in diameter (as shown) and has external threads. Existing lathes are made predominantly with large diameter draw screws that have internal threads. The predominant lathe design is incompatible with the chuck stop taught by Cameron.
U.S. Pat. No. 2,842,371 to Kersten discloses a work-piece holding device. Axial adjustment of the device taught by Kersten to accommodate work-pieces of different thicknesses requires adjustment of three screws. Since adjustment of the each screw affects the angular orientation of the device, adjustment of the screw on one arm 17 would affect the micrometer reading at micrometer receiving bore 49 on the two other arms. Final adjustment of the device to a new axial position requires at least two adjustments of each screw. Moreover screw settings are subject to change during storage of the device.
U.S. Pat. No. 4,262,916 to Tykwinski discloses a chuck having a keep stop and accessories. Tykwinski provides for a work-piece to be supported on a chuck on a centrally disposed rod-like member 76 (FIG. 5) or on the end of a larger diameter cylindrical member 235. The rod like member does not provide a wide support area to ensure that the axis of the work-piece is parallel with the axis of the chuck stop. The cylindrical member limits closure of the chuck stop.
It is also noted that U.S. Pat. No. 2,524,006 to Capallazzi discloses plural discrete spacer members 14 which are secured on the face of the chuck.